As a next generation non-volatile memory to replace flash memories and the like which have limits on a decrease in size, resistance change type memories using a resistance change type element, such as a magnetoresistive random access memory (MRAM), a resistance random access memory (ReRAM), and a phase change random access memory (PCRAM), have attracted an attention.
As a method of increasing a density of a memory (increasing capacity), in addition to a method of decreasing the size of elements themselves constituting the memory, there is a method of converting a recording bit per element into multiple values, and various multivalue methods have been proposed (for example, Patent Documents 1 to 3).
One type of MRAM is referred to as a magnetic domain wall drive type or a magnetic domain wall move type (for example, Patent Document 4). The magnetic domain wall drive type MRAM performs data writing by causing a current to flow in an in-plane direction of the magnetic domain wall driving layer (magnetization free layer), moving a magnetic domain wall using a spin transfer effect by spin-polarized electrons, and reversing magnetization of a ferromagnetic film to a direction of a write current.
In Patent Document 4, methods of multivalue recording and analog recording for a magnetic domain wall drive type MRAM are described.
For MRAMs, different data writing methods have been proposed. For example, in addition to the magnetic domain wall drive type MRAM, a magnetic field writing type MRAM, a yoke magnetic field writing type MRAM, a spin transfer torque (STT) type MRAM, a spin orbit torque (SOT) type MRAM, and the like are known.